DescriptionGastrotheca riobambae is an egg-brooding tree frog with a snout-vent length range of 34.1 – 56.8 mm in males and 48.6 – 66.4 mm in females. In the dorsal view, the snout is round, and from the profile the snout is acutely rounded and protrudes over the jaw. The head is somewhat wider than it is long. The interorbital distance is equal to the eye-nostril distance, approximately 120% of the eyelid width. The first and second fingers are equal in length. The fingers end in small discs that are only slightly wider than the fingers. The tibia is shorter than the foot at about 41% of the snout-vent length (Duellman and Hillis 1987). Their feet are webbed and end in claws (Haas 2003). Their skin is a mixture of areolate and smooth with some patches of granular skin (Duellman and Hillis 1987). Females posses a dorsal egg-brooding pouch that opens on the lower part of their dorsum facing the cloaca (del Pino 1989).

At birth, the tadpoles are about 18 - 20 mm in total length (del Pino 1989), are at stage 33, and have keratinized beaks and denticles, and hindlimb buds (Duellman and Maness 1980). In the dorsal view, the snout is rounded and bluntly rounded from the profile view. There are two alternating rows of labial papillae located across the whole ventral lip. In the profile, the throat is concave. The dorsolaterally directed eyes are large. The distance between the eyes is one-third the width of the head. The cloacal tube is medial. A dorsal fin starts at the posterior edge of the body and gradually grows (Duellman and Hillis 1987).

There are few statistical differences in morphology between different Gastrotheca species, however, G. riobambae, along with G. espeletia and G. pseustes, has smaller discs and shorter tibia than other species of Gastrotheca. Adults and tadpoles of G. riobambae also display a rounder snout than other species that show a more truncated snout structure (Duellman and Hillis 1987).

Gastrotheca espeletia, which was split from G. riobambae in 1987, is similar to G. riobambae in having short limbs and small digital discs. The two can be differentiated by G. riobambae having first and second fingers of the same length and extensive webbing of the feet, while in G. espeletia, the first finger is longer than the second and the feet have less extensive webbing. The snout between the two species also differs with the snout of G. riobambae being rounder and protruding less than in G. espeletia. The tadpoles of G. espeletia also differ from G. riobambae by the former having a dorsal fin that abruptly appears from the body and having labial papillae in a single ventromedial row and in two alternating ventrolateral rows (Duellman and Hillis 1987).

Gastrotheca pseustes was also split from G. riobambae in 1987. They are similar in that both species have small discs, equal length first and second fingers, and short limbs. However, they can be differentiated by the former having a more truncate snout, having less webbing on their feet, and lacking black mottling or spots on the ventrum of the shanks. The tadpoles of G. riobambae can be differentiated from G. pseustes by the former having a concave throat when viewed in profile (Duellman and Hillis 1987).

Similar to other species in the genus Gastrotheca, G. riobambae displays a mixture of brown and green colors. The tympanum is also brown or green in life (Duellman and Hillis 1987).

It is unclear if the following coloration description is in life or in preservative. The majority of individuals (88%) don’t have a pale labial stripe, but most (88%) have a dark canthal stripe. On the back of individuals, there are several green spots of different size delineated by brown color. Often, there is a brown stripe along the green of the body starting from the corner of the frog’s eyes and running across the body. Some individuals have dark brown or green longitudinal paravertebral markings, and in a minority (28%) of specimens there is a pale dorsolateral stripe. On the rare occasion, the dorsal surfaces of the lower leg may be uniform in color, but more frequently they have dark spots and the ventral surfaces are cream with dark spots or mottling. The flanks are pale with dark spots. The anterior surfaces of the thighs range from pale tan to bluish tan and have dark mottling while the posterior surfaces are uniformly pale. Many individuals have a pale supra-anal stripe. The ventrum is cream colored with well-marked dark spots. The vocal sac is grey (Duellman and Hillis 1987).

Individuals differ in coloration, patterning, and size. There are also consistent differences by geography. This variation was so evident that populations in the islands in Laguna Cuicocha were briefly considered a separate species, Gastrotheca cavia, before being returned to G. riobambae in 1987 following allozyme analysis (Duellman and Hillis 1987).

Gastrotheca riobambae is endemic to Ecuador where it has a very broad geographic and altitudinal range. The species is generally confined to the Andes and inter-Andean valleys in north and central Ecuador. Its altitudinal range is 2,200 - 3,500 meters above sea level (Coloma et al. 2004).

The species can more specifically be found on the upper Pacific slopes of the Cordillera Occidental, with an altitude greater than 2600 m, and the Amazonian slopes of the Cordillera Oriental, with an altitude greater than 1800 m (Duellman 1975). The species also occurs in inter-andean valleys, with an altitude above 2300 m, ranging as far south as the slopes of Cerro Tinajillas in Provincia Azuay. Gastrotheca riobambae can be found at elevations of 3860 m in the Paramo de Apagua, 3960 m at Paso de Guamani, and 4135 m on Volcan Antisana. Overall, this species of anuran is restricted to elevations mostly below 3000 m, from the Rio Chanta south to the Riobamba basin (Duellman 1987). The species can also be found in extreme southern Columbia (Duellman 1975).

This species can live in a several different habitats, including wet montane meadows and dry rocky hillsides. Gastrotheca riobambae is most commonly found in pools, streams, drainage, and irrigation ditches, Agave, and cornfields (Duellman 1975).

Life History, Abundance, Activity, and Special BehaviorsGastrotheca riobambae is a terrestrial (Coloma et al. 2006), nocturnal (Roots 2006) species, but has also been found to be active during the day. Females and males are most responsive to the rain, and males can be heard calling on rainy days or nights (Duellman and Maness 1980). Frequently, males call the most right before amplexus begins (Elinson et al. 1990). Male vocalizations consist of long, pulsed calls followed immediately by short pulse groups. The long, pulsed call on its own represents an advertisement call for the female, but the addition of the short, pulsed calls at the end makes the vocalization aggressive towards other males (Sinsch and Juraske 2006).

At 21 degrees Celsius, advertisement calls last an average of 814 ± 16 ms. Their average calling period is 3232 ± 96 ms and their inter-call interval lasts an average of 2419 ± 90 ms. They have an average of 48 ± 1.1 pulses per call at a pulse rate of 61 ± 0.6 Hz. The average dominant frequency is 1.48 ± 0.02 kHz (Sinsch and Juraske 2006).

This species has a long breeding season, and brooding females can be found throughout the year in different parts of their range. However, individual females only reproduce once a year (Duellman and Maness 1980).

Gastrotheca riobambae has a unique reproduction system that is well adapted for terrestrial life. Adult females have a permanent dorsal pouch where eggs are kept during incubation. This pouch is lacking in males and sexually immature females, but is always present in adult females. Compared to the rest of the skin, the pouch is less keratinized, and contains fewer mucous and serous glands (del Pino 1989).

Axillary amplexus occurs on land 24 to 48 hours before eggs are laid and secured in the pouch (del Pino 1989). During reproduction, the female positions herself so that her cloaca is at the same level or above her pouch opening by twisting her hind limbs to elevate her cloaca (Duellman and Maness 1980). As the eggs leave the female's cloaca, the male catches the eggs with his hind feet, fertilizes the egg by passing it near his cloaca or by wiping them in a sperm contain fluid he previously wiped in the space between the female’s cloaca and pouch, the male then places the eggs into the pouch on the female's back with his hind limbs (Duellman and Maness 1980, del Pino 1989). The whole transfer process takes about 6 to 8 hours (del Pino 1989). In a pregnant female, the pouch can extend up to 3 cm anteriorly, and it becomes almost completely transparent during incubation. When the female is ready to give birth, she moves to a body of standing water, braces herself with her front legs, then uses her long toes on her hind legs to reach into the pouch and guide the tadpoles out into the water (del Pino et al. 1975).

During incubation, eggs are about 3 mm in diameter and are a light yellow color (del Pino and Sanchez 1977). The incubation period in the pouch of G. riobambae is variable, lasting between 76 and 120 days (Duellman and Maness 1980). The number of tadpoles born is also variable, but females generally give birth to 81 to 205 tadpoles (del Pino et al. 1975).

A unique characteristic of the embryos in the pouch of G. riobambae is an adaptation called "bell gills." These gills are developed from two paired masses in the tissue that are located on both sides of the head. They begin as small, vascularized discs, and as the embryo grows, the bell gills completely surround the embryo to form a highly vascularized sac (del Pino et al. 1975). This sac is only separated from the pouch by a layer of egg jelly that is 10 µm in thickness. This suggests that the mother provides at least gas and water exchanges to the embryos during incubation, and possibly nutrients. Within 24 hours of birth, circulation to the bells gills ceases, bell gills are reabsorbed, and a new set of secondary gills are formed for use by the tadpole (del Pino 1989).

At birth, the tadpoles are about 18 - 20 mm in total length (del Pino 1989). When they emerge from the pouch, the tadpoles are at gosner stage 33, having keratinized beaks and denticles, and hindlimb buds. Tadpoles are mobile and free feeding at birth. Depending on the site, tadpoles require between 41 days to a year to reach metamorphosis, and the newly formed froglets require about 8 months to one year to become adults (Duellman and Maness 1980).

Trends and ThreatsHistorically, G. riobambae was relatively abundant throughout their range in Ecuador (del Pino 1989). However, in 2004, G. riobambae was listed as “Endangered” by the IUCN due to a drastic population decline, greater than 50%, within the past three generations. While the species has been identified as an adaptable species, the main threats to this species include agriculture, livestock farming and ranching, invasive and problematic species, and pollution (Coloma et al. 2004).

Additionally, climate change has the potential of negatively impacting the remaining habitat of the species by bringing about irregular weather patterns, adding an additional pressure to the survival of communities across their range (Coloma et al. 2004).

It is unlikely that the species’ population decline is due to chytridiomycosis. However, because of the species association with streams, chytrid cannot be completely ruled out as a factor (Coloma et al. 2004).

Relation to HumansGastrotheca riobambae has been used in scientific experiments, especially to look into their unique reproductive behavior, and can also be found in the pet trade where it has a reputation for being hardly and easy to maintain (Wikiri 1996).

In 1987, an analysis of allozymes, morphometrics, and coloration in nine species of Gastrotheca split G. espeletia, G. litonedis, and G. pseustes from G. riobambae and demoted G. cavia back to a population of G. riobambae. The data showed that G. riobambae and G. espeletia were sister species. The clade including the two species was next most closely related to G. ruizi. The next most closely related clade included G. orophylax and G. plumbea. After that, the next most closely related clade included G. litonedis. That data further indicated that G. pseustes was in a different species group, the G. marsupiata group (Duellman and Hillis 1987).

The genus “Gastrotheca” refers to the dorsal brood pouch (Coloma et al. 2004). The species epithet, “riobambae” refers to the species being found in the Riobamba basin (Duellman and Hillis1987).

Gastrotheca riobambae have the smallest embryos among hemiphractids, being only 2.5 to 3 mm in diameter. The cleaving of this species resembles that of a mammalian embryo in slow cleavage and lack of midblastula transition. Slow cleavage, asynchrony, and irregularity of cleavage, all of which are characteristics of G. riobambae, can also be found in other amphibians like the tailed frog, Ascaphus truei. This unique characteristic of slow cleavage is more unique to salamanders than it is to frogs (Elinson et al. 1990).